The use of RFID tags for tracking packages, freight, animals and even humans is well known in the art. Passive RFID tags have a relatively short range and operate in frequency ranges from 100 KHz to 3 GHz. Active RFID tags incorporate a power source to increase the scanning range and typically operate in frequency ranges from 15 Mhz to 3 GHz. The power source is utilized to operate the tag's circuitry and to broadcast a signal to a reader. Passive tags have no internal power source. They draw power from an RF signal transmitted by the reader, which sends out electromagnetic waves that induce a current in the antenna of the tag. In a passive RFID tag, the energy of the received signal is converted into power for control, logic and transmit functions. The transponder modulates the RF carrier signal with a unique code when the transponder is disposed in a position within range of a transmitter and the incident signal has a power greater than a predetermined threshold. Semi-passive tags use a battery to run the chip's circuitry, but communicate by drawing power from the reader. Active and semi-passive tags are useful for tracking high-value goods that need to be scanned over long ranges, such as railway cars or in shipment containers.
The read range of passive tags depends on many factors: the frequency of operation, the power of the reader, interference from other RF devices and the like. In general, low-frequency tags are read from a foot (0.33 meter) or less. High-frequency tags are read from about three feet and UHF tags are read from 10 to 20 feet. Where longer ranges are required, an active tag can boost read ranges to as much as 300 feet or more.
An RFID tag contains a unique code stored in memory that is modulated by an external radio frequency (RF) signal to produce a modulated signal that can be used to uniquely identify the object with which the tag is associated by a receiver. The unique code is contained within read-write, read-only, electronically programmable read only (EPROM or EEPROM) or “write once, read many” (WORM). Read-write RFID tags typically have a serial number that can't be overwritten. Additional blocks of data can be used to store additional information about the items to which the tag is attached, and the memory can be locked to prevent overwriting of data. Read-only RFID tags have information stored on them during the manufacturing process, and such data cannot be altered. WORM tags can have a serial number written to them once, and that information cannot be subsequently overwritten.
In a typical RFID tag, measures are taken to mitigate the effects of external radiation. These include transistor sizing and shielding techniques, and the use of redundant circuit elements as is well known in the art. There are applications, however, where it may be desirable to have RFID tags that are vulnerable to radiation.
Containerized shipments entering the United States must be checked for illicit radiological materials. Currently, more than 11 million cargo containers enter U.S. seaports on an annual basis. To confront an ever increasing threat to national security, Customs and Border Protection (CBP) operates radiation portal monitors at seaports, and uses large scale non-intrusive inspection devices to examine cargo. They have also issued hand-held radiation isotope identifier devices and personal radiation detectors for CBP officers working at ports across the country. These efforts, however, are expensive and ultimately impose an economic burden on commerce.
Since all items within a cargo container either already have or can be expected to have a RFID tag in the near future, the vulnerability to damage from ionizing and non-ionizing radiation can be exploited to provide a means to detect the presence of radiation in an efficient and cheap manner.
In view of the above, there is presently a need to provide a new RFID tag that has components that are vulnerable to radiation so that the presence of such radiation can be easily detected.